Video

Info

Lava Lake Tectonics

Observe the dynamic behavior of a lava lake that provides a tangible analogy to plate motions at tectonic scale in this video courtesy of Dr. Juerg Alean. Watch as the surface crust atop the molten layer of magma flows and transforms over a time scale of a few hours.

To view the Background Essay and Teaching Tips for this video, go to Support Materials below. This resource was developed through WGBH’s Bringing the Universe to America’s Classrooms project, in collaboration with NASA. Click here for the full collection of resources.

Earth’s crust and upper mantle make up the planet’s lithosphere. This rocky layer is broken up into several massive plates that fit together at their boundaries like a jigsaw puzzle. Driven by convection in the viscous mantle below, these plates are in constant motion, moving at rates ranging from less than 2.5 centimeters (1 inch) to over 15 centimeters (6 inches) a year. Where two plates meet, the type of boundary that is created is defined by the motion of the plates. At a convergent boundary, two plates are moving toward one another. At a divergent boundary, the plates are moving apart. At a transform boundary, two plates slide past one another. The theory of plate tectonics describes the motion of Earth’s plates and the role they play in processes such as the drifting and shifting of continents, mountain building, and the formation of new crust in ocean basins. Plate tectonics also explains geological phenomena such as earthquakes—the energy released as two locked plates overcome friction and grind past each other—and volcanoes—the rise of magma as when plates pull apart or collide and are destroyed. Earth’s plates continually interact and shape the surface features of the planet over time. The position and appearance of the continents today are dramatically different from what they were hundreds of millions of years ago!

Erta Ale is one of many volcanoes that lie along a tectonically active region of diverging plates in East Africa. It is an active shield volcano in the Afar region in northeastern Ethiopia, near the border with Eritrea. Typical for a shield volcano, Erta Ale has a characteristic dome shape with gentle sloping sides, a wide base, and very fluid lava flows of basalt. At the summit, 613 meters above sea level, is an elliptical depression (caldera) about 1,600 meters long and 700 meters wide. Within the caldera are two steep-sided “pit” craters; one of the craters is currently filled with molten lava, forming a lava lake.

Lava lakes with persistent or near-persistent activity are very rare—only a handful (fewer than 10) currently exist on Earth. Fed by a magma supply from beneath the volcano, lava lake systems are dynamic, displaying a wide range of behaviors. For example, some lava lakes are constantly circulating and remain filled; in others, the lava may drain and fill up again in cycles.

The behavior of the lava lake at Erta Ale represents a tangible analogy for the larger-scale—and less directly observable—process of plate tectonics. At the surface of the lava lake, a thin crust forms where the lava has cooled and solidified. Agitated by the convecting molten lava, the crust is broken into several pieces—“plates.” The lines of glowing lava represent “plate boundaries.” As convection circulates the molten lava, the “plates” move around, separating or colliding. New lava upwells in some places; in others, slabs of crust sink back into the lava and are destroyed. However, some major differences exist. While tectonic plate motion may be imperceptibly slow (centimeters per year), this lava lake shows very rapid motion (centimeters per second). This 60-second video was filmed over 44 minutes in real time. Also, while the crustal surface layer in volcanic lava lakes moves about on molten lava, the convecting medium driving the motion of Earth’s lithospheric plates is not molten but rather solid, yet viscous.

Visualize phenomena that are too big and too remote to experience or see in a classroom context.

Visualize the abstract concept of plate tectonics.

Provide opportunities for students to observe, ask questions, make evidence-based claims, and develop and use models.

Provide opportunities or contexts for students to transfer their learning about plate tectonics.

Provide experiences that might not otherwise be possible in a classroom (e.g., due to scale, proximity/location, safety).

Engaging students with the phenomena

Before students watch the video, provide dimensions of the lava lake for context/scale and point out the time scale for the video (44 minutes real time, accelerated post processing).

Take this opportunity to dispel common misconceptions about Earth’s interior. Remind students that while analogies exist between the way pieces of the lava lake surface (crust) and Earth’s lithospheric plates move due to convection, Earth’s mantle is not molten.

Encouraging science practices

As students watch the video, have them observe and document evidence of processes analogous to convergence, divergence, and subduction. Students may need to watch the video several times.

Make a claim, using evidence from the video, about the rate of movement of “plates” across the “globe” (the lava lake surface).

Ask students to evaluate the value, and the limitations, of using the lava lake as a model for plate tectonics. How is it similar to and different from larger scale plate tectonics?

Discussion questions

How useful is the Erta Ale lava lake in serving as a model for tectonic plate motion?

What does the lava lake suggest about the dynamic nature of plate tectonics?

How does the lava lake analogy help us understand, or make problematic, the time scales through which plate tectonics operates?